An organic light-emitting device is formed of two opposite electrodes and thin films of organic materials having multilayered semiconductor properties existing therebetween. The organic light-emitting device of the above configuration uses a phenomenon where electric energy is converted into light energy by using an organic material, that is, an organic light emitting phenomenon. In detail, in the structure where an organic material layer is disposed between an anode and a cathode, when a voltage is applied between two electrodes, holes are injected to the organic material layer in the anode and electrons are injected into the organic material layer in the cathode. The injected hole and electron meet each other to form an exciton, and when the exciton is reduced to a ground state, light is emitted.
In the above organic light-emitting device, light that is generated in the organic material layer is emitted through the light transmissive electrode, and the organic light-emitting device may be generally classified into a top emission type, a bottom emission type and a dual emission type. In the case of the top or bottom emission type, one of two electrodes should be a light transmissive electrode, and in the case of the dual emission type, both of the two electrodes should be light transmissive electrodes.
In respect to the organic light-emitting device, many studies have been concentrated since Kodak Co., Ltd. announced that in the case where the multilayer structure is used, the driving at a low voltage is implemented. Recently, a natural color display using the organic light-emitting device is attached to a mobile phone and commercialized.
In addition, a study for the recent organic light-emitting device using a phosphorescent material instead of a known fluorescent material has been progressed, such that efficiency is rapidly improved, and it is expected that the diode would be able to replace a known lighting in the near future.
In order to use the organic light-emitting device for lighting, unlike the known natural color display, the diode should be driven at high brightness, and constant brightness should be maintained like the known lighting. In order to sufficiently improve brightness of the organic light-emitting device, light emission should be implemented in a large area, and in order to implement light emission in the large area, a high driving current should be used. In addition, in order to maintain the constant brightness in the large area, the high current should be uniformly injected into the diode having the large area.
In general, as an anode material of the organic light-emitting device, metal oxide having a large work function is mainly used. However, the electroconductivity of the metal oxide is not relatively high. Accordingly, in the case where the metal oxide is used in an organic EL or an LCD having a small display area, there is no problem, but in the case where the metal oxide is used in an organic EL with a large area which is used for a lighting device, a voltage drop due to a high current is large, such that the current is not uniformly injected into a light emission surface, and therefore light emission of the diode is not uniformly implemented. For example, light emission occurs only around a portion of the electrode that is electrically connected to a driving circuit and weak light emission or no light emission may occur in the remaining region.
Meanwhile, as a cathode material of the organic light-emitting device, a metal having a small work function or an alloy thereof is mainly used. The metal itself may have high electroconductivity, but in the case where transparency of the electrode is required because of characteristics of the organic light-emitting device, if the electrode is formed of a thin film, the electroconductivity is decreased. Accordingly, even in the above case, since the current is not uniformly injected into the light emission surface, light emission of the diode may not be uniformly implemented.
Therefore, in order to use the organic light-emitting device as the lighting device, the light emission of high brightness needs to uniformly occur in the diode having the large area by decreasing resistance of the electrode.
In addition, the decreasing of the resistance of the electrode may also be usefully used in manufacturing of a passive matrix display diode as well as the organic light-emitting device having the large area. Since the passive matrix display does not require an amorphous or poly-silicon thin film transistor back plate, unlike an active matrix, a manufacturing cost is very low. However, recently, since the passive matrix organic EL display has various problems, an active matrix organic EL display rather than the passive matrix organic EL display is rising as a candidate for commercialization. One of the major problems of the passive matrix organic EL display is that the manufacturing of an electrode having excellent light transmittance and electroconductivity in manufacturing of the passive matrix organic EL display diode is an essential technology, but if resistance of the recently used electrode is large and the size of the display is increased by this, a voltage drop in the electrode becomes serious, such that it is difficult to implement a display image.
Accordingly, in an organic light-emitting device field, development of a technology for decreasing resistance of the electrode is required.